Condensation
of circular DNA
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A simple model of a circularly
closed double-stranded DNA in a poor solvent is considered as an example of a semi-flexible
polymer with self-attraction. To find the ground states, the conformational energy is computed as a sum of
the bending and torsional elastic components and the effective self-attraction
energy. The model includes a relative orientation or sequence dependence of
the effective attraction forces between
different pieces of the polymer chain. Two series of conformations are analysed:
a multicovered circle (a toroid) and a multifold two-headed racquet. The
results are presented as a diagram of state. It is
suggested that the stability of particular conformations may be controlled by proper adjustment of the
primary structure. Application of the model to other semi-flexible polymers is considered. |
The
diagram of state. The domains where the conformations shown are ground states
are painted in different colours.
The
bisector (dashed line) marks the case of invariant attraction forces
independent
of the monomer sequence. The upper triangle corresponds
to
stronger attraction for the toroidal parallel arrangement of a polymer chain.
The
lower triangle contains domains where racquets are ground states
because
their special geometry provides enhanced attraction. The relative torsional
stiffness is fixed c = 1.5.
Reference:
E. L. Starostin.
Condensation of circular DNA.
J. Chem.
Phys. 138, 164903 (2013) DOI: 10.1063/1.4802004
Preprint: arXiv:1304.1747